[dpdk-dev] [PATCH v3 04/12] net: add function to calculate a checksum in a mbuf

[Olivier Matz <olivier.matz@6wind.com>]

This function can be used to calculate the checksum of data embedded in
mbuf, that can be composed of several segments.

This function will be used by the virtio pmd in next commits to calculate
the checksum in software in case the protocol is not recognized.

Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
---
 doc/guides/rel_notes/release_16_11.rst |  5 +++
 lib/librte_net/rte_ip.h                | 71 ++++++++++++++++++++++++++++++++++
 2 files changed, 76 insertions(+)

diff --git a/doc/guides/rel_notes/release_16_11.rst b/doc/guides/rel_notes/release_16_11.rst
index 51fc707..fbc0cbd 100644
--- a/doc/guides/rel_notes/release_16_11.rst
+++ b/doc/guides/rel_notes/release_16_11.rst
@@ -104,6 +104,11 @@ New Features
   The config option ``RTE_MACHINE`` can be used to pass code names to the compiler as ``-march`` flag.
 
 
+* **Added a functions to calculate the checksum of data in a mbuf.**
+
+  Added a new function ``rte_raw_cksum_mbuf()`` to process the checksum of
+  data embedded in an mbuf chain.
+
 Resolved Issues
 ---------------
 
diff --git a/lib/librte_net/rte_ip.h b/lib/librte_net/rte_ip.h
index 5b7554a..4491b86 100644
--- a/lib/librte_net/rte_ip.h
+++ b/lib/librte_net/rte_ip.h
@@ -230,6 +230,77 @@ rte_raw_cksum(const void *buf, size_t len)
 }
 
 /**
+ * Compute the raw (non complemented) checksum of a packet.
+ *
+ * @param m
+ *   The pointer to the mbuf.
+ * @param off
+ *   The offset in bytes to start the checksum.
+ * @param len
+ *   The length in bytes of the data to ckecksum.
+ * @param cksum
+ *   A pointer to the checksum, filled on success.
+ * @return
+ *   0 on success, -1 on error (bad length or offset).
+ */
+static inline int
+rte_raw_cksum_mbuf(const struct rte_mbuf *m, uint32_t off, uint32_t len,
+	uint16_t *cksum)
+{
+	const struct rte_mbuf *seg;
+	const char *buf;
+	uint32_t sum, tmp;
+	uint32_t seglen, done;
+
+	/* easy case: all data in the first segment */
+	if (off + len <= rte_pktmbuf_data_len(m)) {
+		*cksum = rte_raw_cksum(rte_pktmbuf_mtod_offset(m,
+				const char *, off), len);
+		return 0;
+	}
+
+	if (unlikely(off + len > rte_pktmbuf_pkt_len(m)))
+		return -1; /* invalid params, return a dummy value */
+
+	/* else browse the segment to find offset */
+	seglen = 0;
+	for (seg = m; seg != NULL; seg = seg->next) {
+		seglen = rte_pktmbuf_data_len(seg);
+		if (off < seglen)
+			break;
+		off -= seglen;
+	}
+	seglen -= off;
+	buf = rte_pktmbuf_mtod_offset(seg, const char *, off);
+	if (seglen >= len) {
+		/* all in one segment */
+		*cksum = rte_raw_cksum(buf, len);
+		return 0;
+	}
+
+	/* hard case: process checksum of several segments */
+	sum = 0;
+	done = 0;
+	for (;;) {
+		tmp = __rte_raw_cksum(buf, seglen, 0);
+		if (done & 1)
+			tmp = rte_bswap16(tmp);
+		sum += tmp;
+		done += seglen;
+		if (done == len)
+			break;
+		seg = seg->next;
+		buf = rte_pktmbuf_mtod(seg, const char *);
+		seglen = rte_pktmbuf_data_len(seg);
+		if (seglen > len - done)
+			seglen = len - done;
+	}
+
+	*cksum = __rte_raw_cksum_reduce(sum);
+	return 0;
+}
+
+/**
  * Process the IPv4 checksum of an IPv4 header.
  *
  * The checksum field must be set to 0 by the caller.
-- 
2.8.1